Fuel injector nozzle manufacturing method

ABSTRACT

A method of manufacturing a fuel injector nozzle where a nozzle seat and a nozzle insert are made using a metal injection molding process. The nozzle seat and the nozzle insert are assembled and bonded together while in their green state. The resulting nozzle assembly is then debinded and sintered to obtain the desired fuel injector nozzle.

CROSS-REFERENCE

This application claims priority to U.S. Provisional Patent Application60/695,013, filed Jun. 30, 2005, entitled “Fuel Injector ManufacturingMethod”, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a manufacturing method for fuelinjector nozzles. The present invention more specifically relates to amanufacturing method for fuel injectors using a metal injection moldingprocess.

BACKGROUND OF THE INVENTION

One of the most critical parts of a fuel injector 10, such as the oneseen in FIG. 1, is the fuel injector nozzle 20. The nozzle 20 iscritical because it is responsible, in part, for the fuel spraycharacteristic which determines the combustion characteristics of theengine.

As engine emission standards become more stringent, so does the need forimproved fuel spray characteristics. This results in more complex fuelinjector nozzle design and tighter dimensional tolerances which makesthe manufacture of this part increasingly difficult, and therefore moreexpensive.

Also, the nozzle 20 needs to interface with the cylinder head 12 of theengine and also receives a needle 22 which acts as a fuel valve. Theseaspects of the nozzle 20 also require precision manufacturing.

An example of such a nozzle is shown in more details in FIGS. 2 and 3.The nozzle 20, which is normally made of metal, has a passage 26 toreceive needle 22. As shown in FIG. 1, the needle 22 is upwardly biasedby spring 24. When biased by the spring 24, the needle 22 sits in thevalve seat 32 to seal the nozzle 20. The nozzle 20 also has at least onefuel passage 42 which communicates at one end with a fuel source and atthe other with passage 26. In the present example, the nozzle 20 hasfour fuel passages 42. As can be seen in FIG. 2, the fuel passages 42communicate with the passage 26 such that fuel entering the passage 26will do so generally tangentially to the wall of the passage 26. Thisconfiguration helps in the formation of the fuel spray droplets.

As can be seen in FIGS. 2 and 3, the complex shape of the fuel passages42 make it very difficult to manufacture the nozzle 20 as a single partby using conventional manufacturing processes such as casting andmachining.

Therefore, the nozzle 20 is usually made in two parts: the nozzle seat30 and the nozzle insert 40. By doing this, at least part of the fuelpassages 42 can be made as grooves in the outer surface 44 of the nozzleinsert 40. When the nozzle insert 40 and the nozzle seat 30 areassembled together, the inner surface 36 of the nozzle seat 30 closesthe grooves to make the fuel passages 42.

In an effort to simplify and to reduce the cost of making the nozzleinsert 40, a manufacturing method known as metal injection molding (MIM)began to be used in recent years. The MIM process allows for aneffective way to manufacture complex and precise parts at a relativelylow cost. The MIM process uses pellets made of fine metal powderscorresponding to the desired material of the part to be made mixedtogether with a polymeric binder.

FIG. 5 illustrates a prior art method of manufacturing a fuel injectornozzle using the MIM process to make the nozzle insert 40. MIM material110 is first heated in order to be injected in a mold shaped in theshape of the nozzle insert 40 at step 115. The part obtained after theinjection molding 115 is know as a “green” part and is slightly largerin size than the final part. The nozzle insert in the green state 120then goes through the debinding process 125 where about 90 percent ofpolymeric binder is removed. The resulting part is known as a “brown”part and is porous. The nozzle insert in the brown state 130 is thensintered at step 135. During the sintering process 135, the nozzleinsert in the brown state 130 is heated thus removing the majority ofthe remaining polymeric binder and causing the metallic powder to fusetogether to form a coherent mass. The sintering 135 also causes the partto shrink to its final size. The resulting nozzle insert 140 then needsto be assembled with the nozzle seat 150.

The nozzle seat 150 is made using more traditional manufacturing methodsince it does not have the same level of complexity as the nozzle insert140. The nozzle insert 140 and nozzle seat are bonded together usingbrazing at step 160. In order to braze the two parts together, plating,usually copper, is applied on the outer surface 44 (FIG. 3) of thenozzle insert 140 prior to assembly 155. After plating 145 of the nozzleinsert 140, the nozzle insert 140 is placed in the nozzle seat 150during the assembly step 155. The nozzle insert 140 and the nozzle seat150 are then brazed together at step 160.

The brazing step 160 has the inconvenient of causing metallic residue tobuildup on the upper surfaces 34 and 46 (FIG. 3) of the assemblednozzle. This residue needs to be removed by secondary machiningoperations at step 165. Once the machining 165 is completed, the finalnozzle assembly 170 is ready to be used in a fuel injector.

Although the process shown in FIG. 5 does allow the manufacture ofcomplex fuel injector nozzles, it is a lengthy process requiringmultiple steps which increase the overall manufacturing cost.

Thus, there exists a need to provide a simplified method ofmanufacturing fuel injector nozzles.

STATEMENT OF THE INVENTION

One aspect of the present invention provides a simplified method ofmanufacturing fuel injector nozzles.

Another aspect of the present invention provides a method ofmanufacturing fuel injector nozzles using metal injection molding.

In another aspect of the invention, a method of manufacturing a fuelinjector nozzle is provided where a nozzle insert and a nozzle seat aremade using MIM. The nozzle insert and the nozzle seat are bondedtogether while in their green state to make a nozzle assembly. Thenozzle assembly is then debinded and sintered.

Yet another aspect of the invention provides a method of manufacturing afuel injector nozzle comprising: metal injection molding a nozzle insertin a green state, metal injection molding a nozzle seat in a greenstate, assembling the nozzle insert and the nozzle seat together whilein their green states to obtain a nozzle assembly, debinding the nozzleassembly, and sintering the nozzle assembly.

In a further aspect, the method further comprises machining at least oneof the nozzle insert and the nozzle seat while in their green states.

In an additional aspect, metal injection molding the nozzle insert andthe nozzle seat is done simultaneously by using a common mold.

In a further aspect, the method further comprises bonding the nozzleinsert and the nozzle seat together while in their green states prior todebinding the nozzle assembly

In yet a further aspect, bonding the nozzle insert and the nozzle seattogether is done by using one of rotational welding, ultrasonic welding,and thermal welding.

In an additional aspect, debinding the nozzle assembly is done by usingone of catalytic debinding, thermal debinding, and solvent debinding.

In another aspect of the invention, a method of manufacturing a singlepart from multiple parts is provided where a first part and a secondpart are made using MIM. The first and the second parts are bondedtogether while in their green state to make an assembly. The assembly isthen debinded and sintered.

Yet another aspect of the invention provides a method of manufacturing asingle part from multiple parts comprising: metal injection molding afirst part in a green state, metal injection molding a second part in agreen state, assembling the first part and the second part togetherwhile in their green states to obtain an assembly, debinding theassembly, and sintering the assembly.

In a further aspect, the method further comprises machining at least oneof the first part and the second part while in their green states.

In an additional aspect, metal injection molding the first part and thesecond part is done simultaneously by using a common mold.

In a further aspect, the method further comprises bonding the first partand the second part together while in their green states prior todebinding the assembly

In yet a further aspect, bonding the first part and the second parttogether is done by using one of rotational welding, ultrasonic welding,and thermal welding.

In an additional aspect, debinding the assembly is done by using one ofcatalytic debinding, thermal debinding, and solvent debinding.

For purposes of this application, the terms “green state” refer to thestate of an injection molded part after the injection molding processand the terms “brown state” refer to the state of a part after goingthrough a debinding process which removes at least a portion of thepolymeric binder found in the part when it is in its “green” state.

Embodiments of the present invention each have at least one of theabove-mentioned aspects, but do not necessarily have all of them.

Additional and/or alternative features, aspects, and advantages of theembodiments of the present invention will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the present invention,reference will now be made to the accompanying drawings by way ofillustration showing a preferred embodiment, in which:

FIG. 1 is a partial cross-sectional view of a fuel injector mounted to acylinder head and having a fuel injector nozzle that can be manufacturedusing the method of the present invention.

FIG. 2 is a top view of the fuel injector nozzle shown in FIG. 1 whichcan be manufactured using the method of the present invention.

FIG. 3 is a cross-sectional view of the fuel injector nozzle of FIG. 2taken along line 3-3.

FIG. 4 is a cross-sectional view of a mold used with the method of thepresent invention.

FIG. 5 illustrates a prior art method of manufacturing fuel injectornozzles.

FIG. 6 illustrates the method of manufacturing a fuel injector nozzle inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described with reference to a fuel injector nozzle.However, it is contemplated that the method described herein can be usedwith any type of nozzles and assemblies having similar manufacturingrequirements as a fuel injector nozzle.

Referring now to FIG. 6, both the nozzle seat 30 and the nozzle insert40 are made using MIM. Various MIM materials 210 can be used dependingon the desired final material.

The MIM material 210 is first heated and then injected into moldscorresponding to the shapes of the nozzle seat 30 and the nozzle insert40. In a preferred embodiment, the injection molding steps 215 are donesimultaneously using a single mold 50 where the mold cavities for thenozzle seat 30 and the nozzle insert 40 are disposed side by side asseen in FIG. 4. The mold 50 has a top portion 52 and a bottom portion54. The top portion has injection gates 56 to allow for the MIM materialto be injected. Vents 58 are provided between the top portion 52 and thebottom portion 54 to allow gases to escape the mold so that no gasbubbles remain in the finished part. It should be understood that thenozzle seat 30 and the nozzle insert 40 can also be molded in separatemolds and that other mold, injection gate, and vent configurations arepossible without departing from the scope of the present invention.

The parts obtained from the injection molding process 215 are a nozzleinsert in the green state 220 and a nozzle seat in the green state 225.Although not necessary, it may be desirable in some circumstances tomachine the parts while their green state at step 226. It is easier tomachine the parts while in their green state because the material issofter and the parts larger than at the end of the manufacturingprocess.

The nozzle insert 220 and the nozzle seat 225 are then assembled (step230) and bonded, preferably using welding (step 235), while in theirgreen state. The preferred welding method is rotational welding.Rotational welding consists in inserting one part inside another whilerotating it such that the friction between the surfaces creates enoughheat to melt the surfaces and create a weld when solidifying. Theadvantage of this type of welding is that the assembly 230 and welding235 steps are done simultaneously. Other welding and bonding methodssuch as ultrasonic welding and thermal welding are possible withoutdeparting from the scope of the present invention. Under certainconditions, the sintering 255 of the nozzle assembly 240, describedbelow, may cause the materials of the nozzle seat 30 and the nozzleinsert 40 to bond together. It is therefore contemplated that thewelding step 235 may be omitted. Under those conditions, and althoughnot necessary, welding (step 235) would improve the bond between the twoparts.

Once the nozzle insert 220 and the nozzle seat 225 are welded, theresulting nozzle assembly 240, which is still in the green state,undergoes a debinding process. During the debinding process, about 90percent of the polymeric binder is removed from the part. The polymericbinder can be removed by using a solvent, applying heat sufficient toremove the binder but not melt the metal powder (thermal debinding), orapplying heat in the presence of a catalyst. The later is known ascatalytic debinding, and is the preferred debinding process. Catalyticdebinding uses lower heat levels than thermal debinding which allows theparts to better maintain their shape and dimensions. The catalyticdebinding process is also faster than the other debinding processesdescribed above.

Once the debinding process 240 has occurred, the resulting nozzleassembly 250 is porous since the majority of the polymeric binder hasbeen removed and is in a state known as the brown state. The nozzleassembly in the brown state 250 then undergoes a sintering process 255,which is the last portion of the manufacturing process. During sintering255, temperature is gradually increased, initially removing theremaining polymeric binder, then causing the metal particles to fuse andbond together. This causes the nozzle assembly 250 to shrink in size.This shrinkage, however, is predictable and the molds are over-sized tocompensate for this shrinkage. This way the final nozzle assembly 260has the desired shape and dimensions. Also, the final nozzle assembly260 requires no further manufacturing steps prior to using it in a fuelinjector. It would however be possible to do so if desired.

This method takes advantage of the MIM process to be able to createcomplex geometries, and by assembling and welding the parts during theirgreen state, the number of operations, and therefore the cost, isgreatly reduced.

Modifications and improvements to the above-described embodiments of thepresent invention may become apparent to those skilled in the art. Theforegoing description is intended to be exemplary rather than limiting.The scope of the present invention is therefore intended to be limitedsolely by the scope of the appended claims.

1. A method of manufacturing a fuel injector nozzle comprising: metalinjection molding a nozzle insert in a green state; metal injectionmolding a nozzle seat in a green state; assembling the nozzle insert andthe nozzle seat together while in their green states to obtain a nozzleassembly; debinding the nozzle assembly; and sintering the nozzleassembly.
 2. The method of claim 1, further comprising machining atleast one of the nozzle insert and the nozzle seat while in their greenstates.
 3. The method of claim 1, wherein metal injection molding thenozzle insert and the nozzle seat is done simultaneously by using acommon mold.
 4. The method of claim 1, further comprising bonding thenozzle insert and the nozzle seat together while in their green statesprior to debinding the nozzle assembly.
 5. The method of claim 4,wherein bonding the nozzle insert and the nozzle seat together is doneby using one of rotational welding, ultrasonic welding, and thermalwelding.
 6. The method of claim 1, wherein debinding the nozzle assemblyis done by using one of catalytic debinding, thermal debinding, andsolvent debinding.
 7. A method of manufacturing a single part frommultiple parts comprising: metal injection molding a first part in agreen state; metal injection molding a second part in a green state;assembling the first part and the second part together while in theirgreen states to obtain an assembly; debinding the assembly; andsintering the assembly.
 8. The method of claim 7, further comprisingmachining at least one of the first part and the second part while intheir green states.
 9. The method of claim 7, wherein metal injectionmolding the first part and the second part is done simultaneously byusing a common mold.
 10. The method of claim 7, further comprisingbonding the first part and the second part together while in their greenstates prior to debinding the assembly.
 11. The method of claim 10,wherein bonding the first part and the second part together is done byusing one of rotational welding, ultrasonic welding, and thermalwelding.
 12. The method of claim 7, wherein debinding the assembly isdone by using one of catalytic debinding, thermal debinding, and solventdebinding.